1. Field of the Invention
The present invention relates to a solid state image sensing device comprising a photosensitive semiconductor element having photocells on a major surface thereof and a colored filter disposed on a major surface of the photosensitive semiconductor element.
2. Description of the Prior Art
In one of conventional designs of color image sensing devices as shown in FIG. 1, there is adhesively attached onto the front of an electron tube type image pickup tube 1, for example, sold under the name of "SACHICON", a color filter 2 consisting of a glass plate and a color coating mounted on the glass plate and comprising gelatin as its predominant component and bearing a checker pattern of the three primary colors. In FIG. 1, a lens is denoted by 3, a cathode by C and a grid by G. In another conventional type of image sensing device, the electron tube of FIG. 1 is replaced by a photosensitve semiconductor element having a substantial number of photocells and a filter carrying a color coating of the three primary colors on a glass plate is attached onto a surface of the semiconductor element in the same manner as in FIG. 1. Yet another type of conventional image sensing device is adapted such that a deposit of gelatin is formed on a major surface of a semiconductor element and desired coloring agents are mixed into the gelatin deposit for the buildup of a color filter having a checker pattern of the three primary colors.
The conventional image sensing devices described above, more particularly, the image sensing devices having the color filter on the major surface of the photosensitive semiconductor element will now be discussed in more detail with reference to FIGS. 2 and 3.
As indicated in FIG. 2, there are formed in a check pattern on a major surface 11a of a silicon substrate 11 a plurality of photocells 12R, 12B and 12G, typically, in the form of well known photodiodes. To complete a semiconductor element 10, a passivation layer 14 of typically PSG film is grown over the major surface 11a of the silicon substrate 11. In FIG. 2, a field oxide layer is denoted by 13, red, blue and green color photocells by 12R, 12B and 12G, respectively.
Subsequently, a water-soluble and photosensitive resin such as gelatin is applied over a major surface 10a of the photosensitive semiconductor element 10 and the resin is removed except on regions thereof where the red color photocells 12R are desired to be formed. Immersing a red dye in the remaining water-soluble photosensitive resin on the major surface 10a of the photosensitive semiconductor element 10 results in developing red color filter layers 15.
An isolation layer 16 is then disposed over the photosensitve semiconductor element 10 bearing the red color filter layers 15 embedded therein. In a manner similar to the manner of developing the red color filter layers 15, a blue dye is immersed into the regions of the water-soluble photosensitive resin on a surface of the isolation layer 16 which correspond to the blue color photocells 12B, thus forming blue color filter layers 17.
Furthermore, another isolation layer 18 is disposed and green color filter layers which each comprises in combination the water-soluble photosensitive resin and a green dye immersed therein are formed in regions of an upper surface of the isolation layer corresponding to the green positions where the green color photocells 12G are to be developed, in the same manner as with the development of the red color filter layers 15 and the blue color filter layers 17.
The last step to complete a solid state image sensing device of a cross-sectional view as shown in FIG. 3 is to dispose a surface protective coating 20 at the uppermost surface of the resulting device. It is noted that the red color filter layers 15, the blue color filter layers 17 and the green color filter layers 19 define as a whole a checker pattern of the three primary colors as is clear from FIG. 4 schematically showing its plan view.
The conventional solid image sensing devices as discussed above are, however, unsatisfactory in the following respects: (a) desired colors are not readily available since the predominant component of the red, blue and green color filter layers 15, 17 and 19, i.e., gelatin is albuminous, in other words, highly sensitive to heat and easily soluble in water or chemicals with a great possibility of blurring and difference in color during dying; (b) the gelatin material in the laminated structure as the predominant component would become molten and reduce in thickness in the event cleaning is done too much on the device prior to patterning for the setup of the red, blue and green color filter layers 15, 17 and 19; and (c) if cleaning is simplified to circumvent this problem, then dust and other pollutants would be left and cause a deficiency in the resulting pattern. Especially, such organic layers are liable to degenerate upon exposure to ultraviolet radiation, thus deteriorating operation life and reliability of the color image sensing device.